Heretofore, a copolymer of tetrafluoroethylene with a fluorinated monomer represented by the following formula, is used for a membrane for electrolysis of sodium chloride or for a membrane or a catalyst layer of a solid polymer type fuel cell. In the following formula, Y is a fluorine atom or a trifluoromethyl group, n is an integer of from 1 to 12, m is an integer of from 0 to 3, p is 0 or 1 and m+p>0.CF2═CF—(OCF2CFY)m—Op—(CF2)n—SO2F
Further, the fluorosulfonyl groups (—SO2F) in the copolymer can be converted to sulfonic groups (—SO3H) by alkali hydrolysis, followed by treatment with an acid.
The sulfonic group-containing polymer (hereinafter sometimes referred to as a sulfonic polymer) is a polymer which is capable of reducing the electric power for electrolysis when used in e.g. an electrolytic cell for sodium chloride in the form of a membrane having a high ion exchange capacity. Further, in a case where such a sulfonic polymer is used for a fuel cell, it is a polymer capable of improving the power generation energy efficiency. And, as such a sulfonic polymer, preferred is a polymer having a larger ion exchange capacity and a lower electric resistance.
However, if it is attempted to increase the ratio of the fluorosulfonyl group-containing monomer to be used for copolymerization for the purpose of increasing the ion exchange capacity of the sulfonic polymer, there has been a problem that the molecular weight of the copolymer tends to be low. A membrane formed of a copolymer having a low molecular weight has had a problem that the mechanical strength and durability are inadequate and as such, is not practically useful.
Further, in the case of a conventional sulfonic monomer, it is required to be copolymerized with tetrafluoroethylene having a high polymerization reactivity in order to obtain a perfluoropolymer having a high molecular weight, and it was impossible to obtain a polymer having a high molecular weight by copolymerization with other perfluoromonomer.
It is an object of the present invention to provide a fluorosulfonyl group-containing compound having a group which can be converted to a sulfonic group and having a high polymerization reactivity and a process for its production, a fluorosulfonyl group-containing polymer having such a compound polymerized, and a sulfonic polymer obtained from such a fluorosulfonyl group-containing polymer.
Further, it is another object of the present invention to provide a fluorosulfonyl group-containing compound having a cyclic structure, which is a monomer satisfying the above object and which has not heretofore been known because of the difficulty in synthesis.